(1) Field of the Invention
The present invention generally relates to processes for removing toxic, hazardous or otherwise undesirable substances from soils, rock, clays, sediments, sludges and aqueous streams. It is particularly concerned with processes for removing toxic, organic substances from soils contaminated by industrial waste products.
(2) Description of the Prior Art
Until recent times, relatively little attention has been paid to the environmental consequences of dumping industrial wastes, whether in designated dump areas or elsewhere. However, as man's understanding of the health hazards associated with many previously dumped substances grows, the pressing need to clean up many contaminated areas has become more and more apparent. Such cleanup operations are, however, very costly as well as technically difficult. They often involve the transportation of large volumes of contaminated materials to specially designated and/or designed dump areas. This transportation of large volumes of contaminated materials, often over relatively long distances, is usually one of the most significant cost factors in cleanup operations of this kind. Moreover, equally large volumes of uncontaminated materials such as soils are often brought from distant locations to refill the cleanup site. At today's prices, the total direct and associated costs of many cleanup operations often exceed $400 per ton of contaminated material. Furthermore, the EPA has announced a five year goal of severely limiting and/or closing most hazardous waste landfills. Consequently, a number of alternatives to transportation intensive cleanup operations have been proposed.
Local incineration and in-situ cleanup processes are the most common alternative cleanup methods. However, the fuel costs of incineration are quite large. Incineration may also lead to air pollution problems which are sometimes even more pernicious than the original soil contamination problem being addressed. In-situ cleanup operations have another set of drawbacks associated with the fact that they usually involve injection of solvents for the contaminating substances and then extract the resulting solvent/contaminant solution by collection wells much in the way secondary and tertiary recovery techniques are carried out in oil field operations. Unfortunately, very large volumes of expensive solvents and/or water are required by such in-situ recovery operations. They present other potential problems as well. Sometimes solvents are lost in fissures in the earth. Such solvents can also, under injection well pressures, wander through various strata in the earth's surface and can themselves become contaminates in distant, previously uncontaminated areas. Solvent contaminant problems of this kind are often dealt with by isolating the contaminated area to be injected from uncontaminated adjacent areas. Walls and screens of one kind or another are usually employed for this purpose. However, the cost of constructing these barriers often becomes prohibitive. Moreover, many contaminated areas are simply missed by these in-situ techniques owing to discontinuities in and/or areas of impermeability of the soil in many contaminated areas.